Nicotiana benthamiana XYLEM CYSTEINE PROTEASE genes facilitate tracheary element formation in interfamily grafting.

Grafting is a plant propagation technique widely used in agriculture. A recent discovery of the capability of interfamily grafting in Nicotiana has expanded the potential combinations of grafting. In this study, we showed that xylem connection is essential for the achievement of interfamily grafting and investigated the molecular basis of xylem formation at the graft junction. Transcriptome and gene network analyses revealed gene modules for tracheary element (TE) formation during grafting that include genes associated with xylem cell differentiation and immune response. The reliability of the drawn network was validated by examining the role of the Nicotiana benthamiana XYLEM CYSTEINE PROTEASE (NbXCP) genes in TE formation during interfamily grafting. Promoter activities of NbXCP1 and NbXCP2 genes were found in differentiating TE cells in the stem and callus tissues at the graft junction. Analysis of a Nbxcp1;Nbxcp2 loss-of-function mutant indicated that NbXCPs control the timing of de novo TE formation at the graft junction. Moreover, grafts of the NbXCP1 overexpressor increased the scion growth rate as well as the fruit size. Thus, we identified gene modules for TE formation at the graft boundary and demonstrated potential ways to enhance Nicotiana interfamily grafting.

Interfamily grafting capacity of petunia.

In grafting, an agricultural technique for propagating flower species and fruit trees, two plants are combined to exploit their beneficial characteristics, such as rootstock disease tolerance and vigor. Grafting incompatibility has been observed, however, between distantly related plant combinations, which limits the availability of plant resources. A high grafting capacity has been found in Nicotiana, belonging to Solanaceae, but not in Ipomoea nil, a Convolvulaceae species. Here, we found that Petunia hybrida, another solanaceous species, has similar ability of interfamily grafting, which indicates that interfamily grafting capability in Solanaceae is not limited to the genus Nicotiana. RNA sequencing-based comparative time-series transcriptomic analyses of Nicotiana benthamiana, I. nil, and P. hybrida revealed that N. benthamiana and P. hybrida share a common gene expression pattern, with continued elevated expression of the ß-1,4-glucanase subclade gene GH9B3 observed after interfamily grafting. During self-grafting, GH9B3 expression in each species was similarly elevated, thus suggesting that solanaceous plants have altered regulatory mechanisms for GH9B3 gene expression that allow tissue fusion even with other species. Finally, we tested the effect of the ß-1,4-glucanase inhibitor D-glucono-1,5-lactone, using glucose as a control, on the interfamily grafting usability of P. hybrida with Arabidopsis rootstock. Strong inhibition of graft establishment was observed only with D-glucono-1,5-lactone, thus suggesting the important role of GH9B3 in P. hybrida grafting. The newly discovered grafting compatibility of Petunia with different families enhances the propagation techniques and the production of flower plants.

Ethylcellulose-based drug nano depots fabricated using a modified triaxial electrospinning.

New strategies based on advanced technologies are highly desired for expanding the applications of biological macromolecules in the applied scientific fields. In the present study, a new kind of core-shell nano depots were designed, in which the shell section was a drug-polymer composite and the core section was a drug reservoir. With ethyl cellulose and ketoprofen as a filament-forming polymeric matrix and a model drug, respectively, a triaxial electrospinning apparatus was developed to conduct both coaxial and triaxial processes, by which monolithic nanofibers F1 and core-shell nano depots F2 were successfully prepared. Although both of them had the same double components, their different nanostructures generated considerable differences in providing drug sustained release profiles. The core-shell nanofiber depots F2 were able to provide a better zero-order drug release profile: no initial burst release, smooth sustained release effect, and smaller tailing-off release for a nice zero-order drug release kinetics. The release percentage (Q) can be linearly manipulated through the release time (t) according to the equation Q2 = 9.40 + 4.74 t (R = 0.9936), providing opportunity for precise administration. The developed strategy and advanced electrospinning technique exhibit a new way for constructing process-structure-performance relationships at nano scale and for expanding the potential applications of biological macromolecules in the applied fields.